1. Field of the Invention
This invention relates to an apparatus and method for supporting a wind-up lay-on roll and, in particular, where the apparatus and method enables the wind-up lay-on roll to apply a substantially uniform force across a width of web material being wound into a roll on a turret assembly.
2. Description of Related Art
When a sheet 2 of webbed material is wound into a roll 4, the sheet 2 generally carries a layer 6 of air into the roll 4. See FIG. 1. At low winding speeds, this layer 6 of air can escape at ends of the roll 4 without causing significant deformations in the sheet 2 during winding. At high speeds of, for instance, 400 to 1200 feet per minute, air is wound into the roll 4 unless precautionary measures are taken.
When air is wound up in a roll 4', air acts as a lubricant between layers 8,10 of the material allowing shifting within consecutive layers particularly near the center or core of the roll 4'. This condition is illustrated in FIGS. 2 and 3 and is commonly referred to as roll telescoping.
Further, when air is wound up in a roll 4", air can become trapped between layers 12,14 of the material. Trapped inside the roll 4", the air forms tires, balloons or bubbles 16, causing deformation and occupying volume as undesired layers. This is illustrated in FIGS. 4 and 5.
Rider or wind-up lay-on rolls are used to "squeeze out" entrapped air from wide webs that are wound into wind-up rolls at high winding speeds to reduce and control the quantity of air wound between layers.
In the manufacture of photographic film, improper winding can cause costly defects. Several coatings which include a photo-sensitive emulsion, backing and abrasion layers are coated on a polyester base sheet having a thickness on the order of 4-7 mils (or 0.004-0.007 inches) and having a width typically 60 inches or more. The coatings are dried. Then the sheet is wound on 6 to 10 inch diameter cores with controlled tensions to suit product type.
The layers on the sheet are sensitive to pressure and abrasion. Therefore, some air entrapment is desired to maintain tension uniformity throughout the roll and to compensate for gauge thickness variation across the web. Too much air can cause slippage between the layers which results in scratches, telescoping, tires, balloons and static build-up during the wind-up or unwind process. Too little air can result in pressure marks.
It is known to wind-up photographic film on cores rotatably mounted on a fixed support or on rotatable arms of turret assemblies. In the case of cores mounted on a fixed support, film accumulators are positioned between the film making operations and the core. Accumulators allow the film making operations to continue when exchanging a first core with a full roll of film on it with an empty second core by taking up the slack of the continuously manufactured film. Accumulators are not necessary with turret assemblies having automatic roll start capabilities. Conventional turret assemblies of this type typically have two cores which are spaced 180 degrees apart. The cores are rotatable about their longitudinal axes and rotatable about an axis of the turret assembly. When film is sufficiently wound on a first one of the cores, the two cores rotate about the turret axis substituting the empty or second core for the first core with the film on it. The film is cut. Then the film is wound on the second core. While the film is being wound on the second core, the first core is removed and replaced with an empty core. This process continues allowing the associated film-making operations to be continuous through the core replacing process.
Conventional designs of rider rolls or wind-up roll lay-on rolls can be described as off-turret assembly and on-turret assembly. Off-turret assembly rider rolls are rider rolls that are mounted on a support that does not rotate with the cores on the turret assembly. On-turret assembly rider rolls are rider rolls that are mounted on a support that does rotate with the cores on the turret assembly.
It is desirable to provide an apparatus and method for maintaining a constant or uniform force across the width of a film while the film is being wound onto a core.
It is also desirable to provide an apparatus and method for maintaining a constant or uniform force across the width of a film being wound on a core when the core becomes full and is rotated, such as, on a turret assembly and replaced with an empty core.
It is another object of this invention to provide an on-turret apparatus and method for supporting a rider or wind-up lay-on roll such that the rider or wind-up lay-on roll applies a substantially uniform force across the width of a film when the film is wound on a first core and after the first core becomes full, when the full core is rotated, such as, on a turret assembly and replaced with an empty core.